Characteristics of Atoms

2. Characteristics of Atoms • Atoms are composed of protons, neutrons, and electrons. • Protons and neutrons are located in the nucleus (center of the atom). • Electrons are located outside of the nucleus. Timberlake LecturePLUS 2000

3. Quantum Model • We learned about: • Dalton’s atomic theory • J.J. Thompson’s plum pudding model of the atom • Rutherford’s model of the atom • Bohr model of the atom • The model used today is called the quantum model

4. Orbitals are represented by a letter (s, p, d, f, …)

10. Describing Electrons • There are two ways to express the number and location of electrons in an atom: • Orbital Diagrams • Electron Configurations Timberlake LecturePLUS 2000

11. Orbital Diagrams • Visual representation of how electrons are placed in orbitals. • Electrons are represented by arrows. • In an orbital diagram, electrons have opposite spins (designated by opposite arrow directions). Timberlake LecturePLUS 2000

12. 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p Increasing energy 3s 2p 2s 1s Blank Orbital Diagram • Fill in the lowest energy orbitals first! Timberlake LecturePLUS 2000

13. Electron Configuration • Tells us the most likely position of where electrons can be found. • It is like the address of an electron. • Electron configurations are used instead of orbital diagrams because they are less cumbersome. Timberlake LecturePLUS 2000

14. Steps for filling in an Orbital Diagram 1. Identify the number of electrons. 2. Fill in the orbital diagram using the following rules: A. Aufbau Principle-Fill in the lowest energy orbitals first. B. Pauli Exclusion Principle-Each orbital (block) can contain 2 arrows. The arrows must be pointed in opposite directions. C. Hund’s Rule Every orbital in a subshell must have one electron in it before any one orbital can be filled with a second electron. Timberlake LecturePLUS 2000

15. Orbital Diagrams:Example #1 • Draw an orbital diagram for H. • Hydrogen has 1 electron. 1s 2s 2p 3s The electron configuration is then: 1s1 Timberlake LecturePLUS 2000

16. Orbital Diagrams:Example #2 • Draw an orbital diagram for B. • Boron has 5 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s22p1 Timberlake LecturePLUS 2000

17. Orbital Diagrams:Example #3 • Draw an orbital diagram for C. • Carbon has 6 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s22p2 Timberlake LecturePLUS 2000

18. Orbital Diagrams:Example #4 • Draw an orbital diagram for O. • Oxygen has 8 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s22p4 Timberlake LecturePLUS 2000

19. Practice Draw an orbital diagram and write the electron configuration for the following elements: 1. He 2. Li 3. N 4. F 5. S Timberlake LecturePLUS 2000

20. He • Helium has 2 electrons. 1s 2s 2p 3s The electron configuration is then: 1s2 Timberlake LecturePLUS 2000

21. Li • Lithium has 3 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s1 Timberlake LecturePLUS 2000

22. N • Nitrogen has 7 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s22p3 Timberlake LecturePLUS 2000

23. F • Fluorine has 9 electrons. 1s 2s 2p 3s The electron configuration is then: 1s22s22p5 Timberlake LecturePLUS 2000

24. S Sulfur has 16 electrons. 1s 2s 2p 3s 3p The electron configuration is then: 1s22s22p63s23p4 Timberlake LecturePLUS 2000

27. More Practice Write the electron configuration for each: A. Cl B. Sr C. I Timberlake LecturePLUS 2000

28. Solution Write the electron configuration for each: A. Cl (17 electrons) 1s2 2s2 2p6 3s2 3p5 B. Sr (38 electrons) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 C. I (53 electrons) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5 Timberlake LecturePLUS 2000

29. Noble Gas Abbreviated Notation He Ne Ar Kr Xe

30. Example • Write the noble gas abbreviated electron configuration for oxygen (O). 1.) The noble gas that occurs before O is He. 2.) Start with [He]. 3.) Finish writing the electron configuration from helium: [He]2s22p4

31. Example • Write the noble gas abbreviated electron configuration for Silicon (Si). • The noble gas that occurs before Si is Ne. • Start with [Ne]. • Finish writing electron configuration from Ne: [Ne]3s23p2

32. Example • Write the noble gas abbreviated electron configuration for Gallium (Ga). • The noble gas that occurs before Ga is Ar. • Start with [Ar]. • Finish writing electron configuration from Ar: [Ar]4s23d104p1

33. Write the Noble-Gas abbreviated electron configuration for the following: a.) S: b.) Cd: c.) Fe: d.) Br:

34. Write the Noble-Gas abbreviated electron configuration for the following: a.) S: [Ne]3s23p4 b.) Cd: [Kr]5s24d10 c.) Fe: [Ar]4s23d6 d.) Br: [Ar]4s23d104p5